This invention relates to a liquid separating composition used for separating the components of a liquid substance under centrifugal force. More particularly, this invention relates to the separation of the relatively light normally liquid blood phase from a blood composition containing serum or plasma from a relatively heavy normally solid blood phase containing, for example, erythrocytes, platelets, etc., by subjecting the blood sample to centrifugation.
Biochemical tests carried out in a clinical laboratory require use of blood serum or plasma as a sample. For preparing the sample for examination, it is necessary to separate the blood serum or plasma from the solid blood components. Prior art methods for obtaining such separation include adding to a sample of blood a substance, or an object, or a combination of the two, having a specific gravity intermediate between serum or plasma and the solid blood component. Under centrifugal forces, this substance moves intermediate between the two types of blood components thereby forming a partitioning wall between them.
Representative wall-forming separation materials include those disclosed in U.S. Pat. Nos. 3,780,935 and 3,852,194, for example. These compositions are referred to as gel compositions or thixotropic compositions. Other patents which are directed to separation and/or barrier materials include, for example, U.S. Pat. No. 4,230,584, issued Oct. 28, 1980; U.S. Pat. No. 4,148,764 issued Apr. 10, 1979; U.S. Pat. No. 4,534,798, issued Aug. 13, 1985; U.S. Pat. No. 4,457,782, issued July 3, 1984; U.S. Pat. No. 4,172,803, issued Oct. 30, 1979; U.S. Pat. No. 4,101,422, issued July 18, 1978 and U.S. Pat. No. 4,310,430, issued Jan. 12, 1982. The '422 patent is directed to a polyester material useful in separation compositions, while the '584 patent is directed to a device for using the composition of the '803 patent. The remaining patents are directed to separation compositions of specific components for achieving specific separation results. None of them, however, are directed to a specific dual resin component as found in this invention which provides good stability of blood analytes and a wide range of groups of drugs.
The invention here, as discussed above, discloses a new thixotropic composition which may, for example, be useful for the improved recovery of imipramine. In the ideal separation of the type employing a thixotropic gel as the phase separation barrier component, the gel is characterized as compositionally stable, and physically stable in the absence of any substantial application of centrifugal force. Moreover, it is appropriate for the gel to form a strong cohesive barrier between the components desired to be separated, that the gel be chemically inert, and have a density which is intermediate that of the blood phases to be separated.
Compositionally stable compositions mean that the components are ingredients of the separating gel which will not separate under normal storage and/or use. The composition is basically an oil or an oil-like composition compounded with an inert filler. However, the composition should be stable enough that the oil or oil like material does not bleed or separate from the inert filler dispersed therein. Physically stable barrier materials will not move or change shape except when subjected to the application of centrifugal force. By chemically inert, it is meant that the barrier material should not be chemically reactive with the blood sample being separated, its constituents or reagents commonly employed in carrying out diagnostic testing of blood serum.
This invention constitutes an improvement over the prior art thixotropic gel compositions in that it has been discovered that a specific hydrocarbon resin such as poly-alpha-pinene has hydrophobic properties and gives superior recoveries for drugs with higher PKa values. However, this hydrocarbon resin has a lower density of about 0.99 which restricts the use of this material alone as being a possible candidate for a barrier gel. The Applicants here have discovered, quite unexpectedly, that by mixing a chlorinated hydrocarbon with this hydrocarbon to form a dual resin component, the density is increased to a level to formulate a thixotropic gel appropriate for centrifugal separation. Moreover, with this hydrocarbon and chlorinated hydrocarbon blend, adjustments can be made of the density of the final resin component as required for specific applications.
In considering generally the properties of the gel composition of the invention here, the composition contains a mixture of resin blends, as discussed above, with an adjusted specific gravity, preferably, ranging from within the range of between about 1.00 and 1.04 at 25.degree. C., a radiation stabilizer, a short chain polyfunctional material as a network stabilizer and a thixotropic agent. The composition of the invention has a specific gravity at 25.degree. C. generally within the range of between about 1.03 and 1.07, and a viscosity at 25.degree. C. of within the range of between about 800,000 and 1,800,000 centipoises at a shearing rate of 1 second.sup.-1.
The new gel composition is based upon hydrocarbon raw materials selected because they are more hydrophobic, in combination. Moreover, the new gel composition has a lower specific gravity and a higher viscosity. The new gel composition forms a complete and solid barrier with minimum red cell entrapment at 1,000 G force centrifugation. It provides the stability of blood analytes. Moreover, it provides good drug recovery and stability of a wide range of drugs.
In considering generally the composition for the invention here, a typical composition includes a resin blend, as discussed above, of a polyterpine resin and a chlorinated alpha olefin. The composition includes a radiation stabilizer such as Gamma Shield 401 or 801, products of M. & T. Chemicals Inc., Rahway, N. J., or epoxidized soybean oil, a network stabilizer such as glycerine, ethylene diamine, propylene glycol, or ethylene glycol, a thixotropic agent such as silica and a pigment such as titanium dioxide.
A preferred composition, in accordance with this invention, includes admixing within the range of between about 67 and 86 percent by weight polyterpine, within the range of between about 13 and 24 percent by weight chlorinated hydrocarbon, within the range of between about 2 and 6 percent by weight silica, within the range of between about 0.15 and 0.8 percent a short chain polyfunctional stabilizer, within the range of between about 0.015 and 0.03 percent titanium dioxide, and within the range of between about 2.3 and 15 percent epoxidized soybean oil. The chlorinated hydrocarbon used in the composition is selected to have a minimum of 50 percent chlorine. A specific source of the polyterpine resin (poly-alpha-pinene) is a product of Arizona Chemical Company designated Zonarex Alpha 25. A specific source of chlorinated hydrocarbon is DO8618 which is chlorinated octadecene, a product of Dover Chemical Corporation.